1. Field of the Invention
This invention relates to room temperature-vulcanizable polyorganosiloxane compositions. More particularly, this invention relates to room temperature, vulcanizable polyorganosiloxane compositions having a surface that can be readily coated with paint following room temperature vulcanization.
2. Description of the Prior Art
It is known that a hydroxyl-terminated polyorganosiloxane can be vulcanized or cured at room temperature to form an elastomer by reacting it with an organosilicon compound containing amido groups and/or an organosilicon compound containing aminoxy groups as the curing agent. Typically such room temperature curable compositions contain both a bifunctional curing agent and one containing three or more amide or aminoxy groups per molecule. By varying the ratio of these two types of curing agents it is possible to obtain a wide range of properties in the cured elastomer, from low modulus--high elongation to high modulus--low elongation. In particular, low modulus--high elongation compositions are widely used as sealants by the construction industry because these products exhibit excellent weather and fatigue resistance. Japanese Patent Publication (Kokai) No. 56[81]-86951, which was published on July 15, 1981, discloses compositions of this type which contain an aminoxy-substituted organosilicon compound in addition to an alcohol that is added to achieve curing only at the surface of the composition while the interior portion remains uncured.
The most significant drawback of the sealants disclosed in the preceding paragraph is that the surface of the cured sealant is either difficult to coat with paint or cannot be painted. For the purpose of this invention, paintability or coatability is defined as the ability of a paint to coat and adhere to a surface. Although silicone rubber sealants possess excellent properties, they are limited in their applications because of poor paintability.
U.S. Pat. No. 4,358,558, which issued to C. Shimizu on Nov. 9, 1982 from application Ser. No. 334,014 filed Dec. 23, 1981, discloses room temperature curable polyorganosiloxane compositions which are paintable in the cured state and which contain a silanol-terminated polydiorganosiloxane having a viscosity of from 1.times.10.sup.-4 to 0.2 m.sup.2 /sec. at 25.degree. C., an organosilicon compound containing an average of more than 2 aminoxy groups per molecule, an inorganic filler and a primary or secondary alcohol containing acetylenic unsaturation, i.e., a carbon-to-carbon triple bond. The alcohol is considered indispensible for obtaining a cured material wherein the internal portion exhibits a degree of elasticity characteristic of a sealant and the exposed surfaces are sufficiently adhesive to be coatable with paints as defined hereinbefore.
It is an objective of this invention to define curable polyorganosiloxane compositions exhibiting coatability with various types of paints following curing.